In the 18th century, rural uprisings swept across Vietnam, yet most were easily subdued. However, in 1771, three brothers from Tay Son village, near Quy Nhon, led a rebellion that would reshape the nation. With widespread support from displaced peasants, ethnic minorities, small merchants, and urban dwellers, the Tay Son movement promoted ideals of equality, justice, and liberty. Gaining momentum in the south, the Tay Son army attracted further backing by redistributing land from the wealthy to the poor. By mid-1786, they had overthrown both the Trinh and Nguyen lords, leaving the Le dynasty in name only.

When the Le king requested Chinese assistance in 1788 to oust the Tay Son, the Chinese occupied Hanoi. In response, Nguyen Hue, the middle Tay Son brother, proclaimed himself Emperor Quang Trung. Leading his army on a rapid 600-kilometer march from Hue, he decisively defeated the Chinese forces at Dong Da near Hanoi. Establishing Hue as his capital, Emperor Quang Trung began enacting reforms to unify the country, but his death in 1792 at just 39 left the throne vulnerable, and his young son was unable to secure power.

Meanwhile, one surviving Nguyen lord, Prince Nguyen Anh, sought to reclaim the throne. After several failed attempts, he retreated to Phu Quoc Island, where he met French bishop Pigneau de Béhaine. Eager to secure future religious and trade opportunities, the bishop agreed to seek French support on behalf of Nguyen Anh. Though a formal treaty was signed in 1787 promising military aid in exchange for territorial concessions, France, mired in financial crisis, could not fulfill its promise. Undeterred, Pigneau de Béhaine assembled a force of four thousand mercenaries and several ships, launching an expedition in 1789. Nguyen Anh eventually captured Hanoi in 1802, ascending as Emperor Gia Long, founder of the Nguyen dynasty. Though Pigneau de Béhaine passed away in 1799, his significant role was honored with a grand funeral.